The invention relates to magnetoresistive sensors for angle measurements. A preferred field of application of magnetoresistive sensors is their use for contactless angle measurement.
Magnetoresistive sensors for angle measurements such as, for example, the sensors of the type KMZ 41, manufactured and marketed by Philips Semiconductors, are principally known and utilize the magnetoresistive effect. A preferred use of MR sensors is in the weak field, angle and rotation measurements and in Magnetic Force Microscopy measurements (abbreviated MFM measurements; for example, on crystals of the product marketed as KMZB34 by Philips Semiconductors).
Magnetoresistive sensors (also abbreviated to and known as MR sensors) for angle measurements operate in the saturation range, i.e. they utilize the effect that a sufficiently strong external magnetic field H rotates an internal magnetization M of the sensor elements in the arrangement of the magnetoresistive sensor in a (substantially) fully parallel direction. In the case of said sensor KMZ 41, the magnetic field strength of the external magnetic field required for full alignment of the internal magnetization is 70 to 100 kA/m. The generation of such a strong magnetic field requires a relatively high number of constructive components. A reduction of this high field strength is desirable.
It is an object of the invention to achieve a decrease of the magnetic field strength required for saturation (parallel setting).
To achieve this object, an easier rotatability of the magnetization of the MR sensor elements must be obtained. According to the invention, this is achieved by a magnetic field-sensitive sensor arrangement comprising a sensor element of NiFe material which is substantially arranged in a plane and is substantially strip-shaped in this plane, said material having an at least substantially elliptical and/or tapering contour at its ends in this plane, and a substantially circular trigger element of NiFe material which is arranged in said plane adjacent to at least one of the strip-shaped sensor elements and is insulated therefrom. Particularly, the trigger structure comprising the substantially circular, electrically uncontacted trigger element of NiFe material contributes to achieving the object.
The rotatability of the magnetization may be fundamentally increased, on the one hand, by way of the design of the MR sensor elements and, on the other hand, by realization of the circular trigger structure. Due to its circular shape, the trigger structure provides the principally easiest rotatability of the magnetization; this rotation can thus be effected by weak magnetic fields. It is therefore obvious to realize the sensor elements also in a circular shape. However, this has the drawback that-conditioned by manufacturing spreads (mask adjustment in photolithography, etc.)-such circular structures can only be contacted very incompletely, i.e. with inadmisibly high manufacturing tolerances, and, moreover, require a large surface area.
The invention is therefore useful to the extent that a circular structure which is not electrically connected to the rest of the sensor elements does not only have the very satisfactory rotatability of the magnetization but also transfers this rotatability to the adjacent MR sensor elements due to electrostatic interaction. In other words, the invention utilizes the electrostatic interaction of sensor elements which are arranged spatially close together, with a resultant influence of the direction of magnetization (i.e. the domain structure of the NiFe material). When the lateral distance between the trigger structure, i.e. the substantially circular trigger element of NiFe material, and the subsequent MR sensor elements is sufficiently smallxe2x80x94it should be as small as is constructively possiblexe2x80x94, then there is an electrostatic influence on the trigger structure and the sensor elements, which significantly enhances the rotatability of the magnetization in the adjacent sensor elements, namely by a reduction of the shape-anisotropy field strength. When the distance between subsequent MR sensor elements is also small at the most adjacent location, i.e. when it is preferably approximately the same as the distance between the trigger structure and the first MR sensor element, and when the separate sensor elements have a length whose value, starting from that of the sensor element which is directly adjacent to the trigger structure, i.e. the substantially circular trigger element of NiFe material, increases continuously from sensor element to sensor element, the easy rotatability of the magnetization of the substantially circular trigger element of NiFe material is transferred to the whole sensor, i.e. the overall arrangement of sensor elements.
The invention has the advantage that the magnetic field strength of the external magnetic field (also denoted as xe2x80x9csaturation field strengthxe2x80x9d) required for full alignment of the internal magnetization can be realized with simple, constructive means and that, for example, a reduction of the required saturation field strength to 20-30 kA/m can be achieved for the magnetoresistive sensors of the types described in the opening paragraph. The invention has the further advantage that this effect is not influenced by manufacturing spreads.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.